diff --git a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexMetaDataFrame.java b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexMetaDataFrame.java
index 9e95970..b48ded4 100644
--- a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexMetaDataFrame.java
+++ b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexMetaDataFrame.java
@@ -47,4 +47,9 @@
 	
 	// Set special validity flag.
 	public void setValid(boolean isValid);
+	
+	// Special placeholder for LSN information. Used for transactional LSM indexes.
+	public long getLSN();
+	
+	public void setLSN(long lsn);
 }
diff --git a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/LIFOMetaDataFrame.java b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/LIFOMetaDataFrame.java
index 31c674d..1b8bc15 100644
--- a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/LIFOMetaDataFrame.java
+++ b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/LIFOMetaDataFrame.java
@@ -36,6 +36,7 @@
 	protected static final int levelOff = maxPageOff + 12; //20
 	protected static final int nextPageOff = levelOff + 1; // 21
 	protected static final int validOff = nextPageOff + 4; // 25
+	protected static final int lsnOff = validOff + 4; // 29
 
 	protected ICachedPage page = null;
 	protected ByteBuffer buf = null;
@@ -101,7 +102,7 @@
 	@Override
 	public void initBuffer(byte level) {
 		buf.putInt(tupleCountOff, 0);
-		buf.putInt(freeSpaceOff, validOff + 4);
+		buf.putInt(freeSpaceOff, lsnOff + 4);
 		//buf.putInt(maxPageOff, -1);
 		buf.put(levelOff, level);
 		buf.putInt(nextPageOff, -1);
@@ -131,4 +132,14 @@
             buf.putInt(validOff, 0);
         }
     }
+
+    @Override
+    public long getLSN() {
+        return buf.getLong(lsnOff);
+    }
+
+    @Override
+    public void setLSN(long lsn) {
+        buf.putLong(lsnOff, lsn);
+    }
 }
diff --git a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java
index edc9b4d..b7ed45b 100644
--- a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java
+++ b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java
@@ -1,5 +1,11 @@
 package edu.uci.ics.hyracks.storage.am.lsm.common.api;
 
+import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
+
 public interface ILSMIOOperationCallback {
-    public void callback();
+    public void beforeOperation(ILSMIOOperation operation) throws HyracksDataException;
+    
+    public void afterOperation(ILSMIOOperation operation, Object newComponent) throws HyracksDataException;
+    
+    public void afterFinalize(ILSMIOOperation operation, Object newComponent) throws HyracksDataException;
 }
diff --git a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallbackFactory.java b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallbackFactory.java
new file mode 100644
index 0000000..52361ee
--- /dev/null
+++ b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallbackFactory.java
@@ -0,0 +1,7 @@
+package edu.uci.ics.hyracks.storage.am.lsm.common.api;
+
+import java.io.Serializable;
+
+public interface ILSMIOOperationCallbackFactory extends Serializable {
+    public ILSMIOOperationCallback createIOOperationCallback(Object syncObj);
+}
diff --git a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallback.java b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallback.java
index 47f556d..53e7224 100644
--- a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallback.java
+++ b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallback.java
@@ -1,21 +1,33 @@
 package edu.uci.ics.hyracks.storage.am.lsm.common.impls;
 
+import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
+import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperation;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperationCallback;
 
 public class BlockingIOOperationCallback implements ILSMIOOperationCallback {
 
     private boolean notified = false;
 
-    @Override
-    public synchronized void callback() {
-        this.notifyAll();
-        notified = true;
-    }
-
     public synchronized void waitForIO() throws InterruptedException {
         if (!notified) {
             this.wait();
         }
         notified = false;
     }
+
+    @Override
+    public void beforeOperation(ILSMIOOperation operation) throws HyracksDataException {
+        // Do nothing.
+    }
+
+    @Override
+    public void afterOperation(ILSMIOOperation operation, Object newComponent) throws HyracksDataException {
+        // Do nothing.
+    }
+
+    @Override
+    public synchronized void afterFinalize(ILSMIOOperation operation, Object newComponent) throws HyracksDataException {
+        this.notifyAll();
+        notified = true;
+    }
 }
diff --git a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ImmediateScheduler.java b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ImmediateScheduler.java
index bd690ac..c84a852 100644
--- a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ImmediateScheduler.java
+++ b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ImmediateScheduler.java
@@ -16,8 +16,6 @@
             e.printStackTrace();
         } catch (IndexException e) {
             e.printStackTrace();
-        } finally {
-            operation.getCallback().callback();
         }
     }
 
diff --git a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java
index 837616a..634800a 100644
--- a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java
+++ b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java
@@ -106,14 +106,20 @@
         if (LOGGER.isLoggable(Level.INFO)) {
             LOGGER.info("Flushing LSM-Index: " + lsmIndex);
         }
-        Object newComponent = lsmIndex.flush(operation);
-
-        // The implementation of this call must take any necessary steps to make
-        // the new component permanent, and mark it as valid (usually this means
-        // forcing all pages of the tree to disk, possibly with some extra
-        // information to mark the tree as valid).
-        lsmIndex.getComponentFinalizer().finalize(newComponent);
-
+        Object newComponent = null;
+        try {
+            operation.getCallback().beforeOperation(operation);
+            newComponent = lsmIndex.flush(operation);
+            operation.getCallback().afterOperation(operation, newComponent);
+            
+            // The implementation of this call must take any necessary steps to make
+            // the new component permanent, and mark it as valid (usually this means
+            // forcing all pages of the tree to disk, possibly with some extra
+            // information to mark the tree as valid).
+            lsmIndex.getComponentFinalizer().finalize(newComponent);
+        } finally {
+            operation.getCallback().afterFinalize(operation, newComponent);
+        }
         lsmIndex.resetInMemoryComponent();
         synchronized (diskComponentsSync) {
             lsmIndex.addFlushedComponent(newComponent);
@@ -175,21 +181,28 @@
         AtomicInteger localSearcherRefCount = searcherRefCount;
 
         List<Object> mergedComponents = new ArrayList<Object>();
-        Object newComponent = lsmIndex.merge(mergedComponents, operation);
+        Object newComponent = null;
+        try {
+            operation.getCallback().beforeOperation(operation);
+            newComponent = lsmIndex.merge(mergedComponents, operation);
+            operation.getCallback().afterOperation(operation, newComponent);
+            
+            // No merge happened.
+            if (newComponent == null) {
+                isMerging.set(false);
+                return;
+            }
 
-        // No merge happened.
-        if (newComponent == null) {
-            isMerging.set(false);
-            return;
+            // TODO: Move this to just before the merge cleanup and remove latching on disk components
+            // The implementation of this call must take any necessary steps to make
+            // the new component permanent, and mark it as valid (usually this means
+            // forcing all pages of the tree to disk, possibly with some extra
+            // information to mark the tree as valid).
+            lsmIndex.getComponentFinalizer().finalize(newComponent);
+        } finally {
+            operation.getCallback().afterFinalize(operation, newComponent);
         }
-
-        // TODO: Move this to just before the merge cleanup and remove latching on disk components
-        // The implementation of this call must take any necessary steps to make
-        // the new component permanent, and mark it as valid (usually this means
-        // forcing all pages of the tree to disk, possibly with some extra
-        // information to mark the tree as valid).
-        lsmIndex.getComponentFinalizer().finalize(newComponent);
-
+        
         // Remove the old Trees from the list, and add the new merged Tree(s).
         // Also, swap the searchRefCount.
         synchronized (diskComponentsSync) {
@@ -202,6 +215,7 @@
             }
             searcherRefCount.set(0);
         }
+        
 
         // Wait for all searchers that are still accessing the old on-disk
         // Trees, then perform the final cleanup of the old Trees.
diff --git a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java
index 1e51b41..24bd16c 100644
--- a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java
+++ b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java
@@ -1,12 +1,24 @@
 package edu.uci.ics.hyracks.storage.am.lsm.common.impls;
 
+import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
+import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperation;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperationCallback;
 
 public enum NoOpIOOperationCallback implements ILSMIOOperationCallback {
     INSTANCE;
 
     @Override
-    public void callback() {
+    public void beforeOperation(ILSMIOOperation operation) throws HyracksDataException {
+        // Do nothing.
+    }
+
+    @Override
+    public void afterOperation(ILSMIOOperation operation, Object newComponent) throws HyracksDataException {
+        // Do nothing.
+    }
+
+    @Override
+    public void afterFinalize(ILSMIOOperation operation, Object newComponent) throws HyracksDataException {
         // Do nothing.
     }
 }
diff --git a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ReferenceCountingOperationTracker.java b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ReferenceCountingOperationTracker.java
index 71a178c..5b10ba3 100644
--- a/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ReferenceCountingOperationTracker.java
+++ b/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/ReferenceCountingOperationTracker.java
@@ -2,6 +2,7 @@
 
 import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
 import edu.uci.ics.hyracks.storage.am.common.impls.NoOpOperationCallback;
+import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperation;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperationCallback;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIndex;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIndexAccessor;
@@ -53,7 +54,17 @@
 
     private class FlushOperationCallback implements ILSMIOOperationCallback {
         @Override
-        public void callback() {
+        public void beforeOperation(ILSMIOOperation operation) throws HyracksDataException {
+            // Do nothing.
+        }
+
+        @Override
+        public void afterOperation(ILSMIOOperation operation, Object newComponent) throws HyracksDataException {
+            // Do nothing.
+        }
+
+        @Override
+        public void afterFinalize(ILSMIOOperation operation, Object newComponent) throws HyracksDataException {
             ReferenceCountingOperationTracker.this.notifyAll();
         }
     }
diff --git a/hyracks-storage-am-lsm-rtree/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/rtree/impls/AbstractLSMRTree.java b/hyracks-storage-am-lsm-rtree/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/rtree/impls/AbstractLSMRTree.java
index 7711a89..57fd2db 100644
--- a/hyracks-storage-am-lsm-rtree/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/rtree/impls/AbstractLSMRTree.java
+++ b/hyracks-storage-am-lsm-rtree/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/rtree/impls/AbstractLSMRTree.java
@@ -60,7 +60,7 @@
 
 public abstract class AbstractLSMRTree implements ILSMIndexInternal, ITreeIndex {
 
-    public class LSMRTreeComponent {
+    public static class LSMRTreeComponent {
         private final RTree rtree;
         private final BTree btree;